Thickening apparatus for fibrous suspensions



Jan. 5, 1960 w. ENGEL ETAL 2,919,751.

THICKENING APPARATUS FOR FIBROUS SUSPENSIONS Filed Sept. 16, 1955 2 Sheets-Sheet A Fig. 2

INVEN T015 W/LLY E/VGEL WOLFGANG BREW/v05? BY THEODOR w LE/TZ Attorneys FiledSept. 16, 1955 Jan. 5, 1960 w. ENGEL ETA}; 2,919,751

THICKENING APPARATUS FOR FIBROUS sUsPENsIoNs 2 Sheets-Sheet 2 INVENTOR. WILL) ENGEL WOLFGANG BREUlV/NGER BY THEODOR n! LE/TZ Attorneys United States PatentOf" THICKENING APPARATUS FOR FIBROUS SUSPENSIONS Willy Engel, Aarau, Switzerland, and Wolfgang Breuninger and Theodor W. Leitz, Heidenheim, Brenz, Germany, assignors to J. M. Voith G. m. b. H.,' Maschinenfabrik, Heidenheirn, Brenz, Germany Application September 16, 1955, Serial No. 534,788

Claims priority, application Germany September 18, 1954 4 .Claims. 01. 162-308) The invention relates to a thickening apparatus for removing excess liquid from fibrous suspensions as used drum strainer or cylindrical screen which is in contact over a certain portion of its cylindrical surface with a machine wire or wire cloth, the water being removed from the pulp stock by being pressed between the cylinder and the wire surface. These known devices suifer from the drawback that a machine wire is usually not sufliciently adaptable to be subjected to a tension adequate to bring about a greater pressure on the cylinder. Consequently, the final content of dry matter of the suspension is relatively low.

Therefore, it has also been suggested to use an endless wire cloth made of an elastic material such as rubber with the drum strainer in order to achieve a higher pressure between the wire and the cylindrical drum surface.

Moreover, in order to obtain a further increase in the final dry content of a pulp stock, it is known in the art to use several thickeners, each containing a drum strainer, in successive order. This known arrangement has the drawback that it is necessary to intermediately part or, lift the web from the wire after passing it through a first thickener in order to enter it into the next following thickener. This intermediary parting presents considerable difficulty with most materials and with certain materials it is completely impossible to carry out the parting step.

It is an object of our invention to provide a thickening "apparatus which permits the obtaining of a very high percentage content of dry matter in thickened fibrous suspension while protecting the fibers to the highest degree possible.

It is another object of this invention 'to provide a thickening apparatus which eliminates the necessity of an intermediary parting of the Web.

It is yet another object of this invention to provide a thickening apparatus wherein the surface pressure on the fibrous material can be regulated in consonance with the moisture content of the fiber web, pressure being increased with decreasing moisture content.

In order to achieve the aforesaid and other objects and advantages, we have invented a thickening apparatus for fibrous suspension which comprises at least two drum strainers and only one endless cloth or felt which is made of'an elastic material such as, for instance, rubber. In our invention, the endless cloth is pressed by means of hitch rolls or stenting rolls against the curved surface of the strainer so as to press out the water from the pulp stock. Our invention provides for the use of an impermeable cloth or a permeable wire made of an elastic material.

It is an essential advantage of this arrangement, ac-

2,919,751 Patented Jan. 5, 1960 cording to our invention, that a very high final dry content can be obtained, even from suspensions from which the removal of the liquid is difficult to achieve.

Another advantage resides in the fact that the intermediate parting or lifting of the web from a first cloth and its entering into another thickener is made superfiuous.

The apparatus according to the invention has the further advantage that only one stenting or tensioning device for the cloth is required with two or more drum strainers. The number of wire or guide rolls can also be correspondingly smaller and the entire apparatus is of a less complicated construction.

According to a further feature of the invention, the diameters of the drum strainers successively following the first one in the direction of movement of the pulp stock, can be made consecutively smaller. Thereby, the surface pressure on the second and the following drums is always somewhat greater than the pressure on the next preceding drum and a higher dry content is obtained. By a suitable selection of the drum diameters, the surface pressure on the individual drums can be regulated in such a manner that the suspension on the first cylinder, where the moisture content of the stock is high, is subjected to the least surface pressure, while a greater pressure is exerted on the fiber web when reaching the second cylinder where the web already has an increased content of dry matter and correspondingly a greater strength. If the pressure were too great on the first drum, the stock having the higher initial moisture content might be squashed out from between the cloth and the drum at the lateral edges thereof.

We have found that optimal conditions of pressure are obtained when the ratio of the larger, i.e., the preceding, to the smaller, i.e., the next following, drum is in the order of 3:2 to 5:2.

The efliciency of the apparatus according to our invention is further increased by another feature which provides that a hitch-roll is arranged in cooperation with at least one drum strainer so as to exercise additional pressure on the stock between the drum and the endless wire. We have found that this permits a still-further increase in the final dry content of the stock.

Of course, the pressure along the line of contact between the hitch-roll and the drum will be adjusted to the particular properties of the pulp stock. Thus, some stocks permit the use of a higher pressure, while others will only permit the use of a lower one. This depends largely on the dry content of the web at the contact line in question. The higher the dry content, the greater will usually be, in most cases, the pressure that can be applied to the material forming the web.

For this same reason it is preferable to disclose the hitch-roll with the second or another subsequent drumstrainer, and not with the first one. The dry content o'fthe web in the range of the drums following the first cylinder will be greater, a higher pressure along the line of contact between hitch-roll and drum can be applied and, consequently, a considerably higher final content of dry matter is obtained. Depending upon the kind of fibrous material in the pulp stock, the pressure applied to the web on the second cylinder may, in some cases, be approximately twice the pressure that could be applied to the same material on the first cylinder.

In a preferred embodiment of the apparatus according to our invention, the constructionis further simplified by using one of the cloth-reversing or end rolls such as the 'hitch or stenting roll. Thereby no special hitch-roll need roll can be displaced in the direction toward and away from the drum strainer. The hitch-roll may be urged against the cylinder surface exclusively by the tension of the elastic endless cloth or an additional pressure device such as air-pressure pump may be provided for further increasing the contact pressure between the cylinder and the cloth reversing and stenting roll.

In a further preferred embodiment according to the invention, this double-purpose roll for stenting and concurrently reversing the cloth is hingedly mounted so that it can be pivoted into contact with the surface of its corresponding drum strainer and is simultaneously provided with a pressure adjusting device which permits causing pressure to be exercised by the double-purpose roll on the pulp stock to be thickened, or permits the lifting of the roll off the cylinder against the tension of the elastic endless clo'th. In this embodiment, the double purpose roll may either act as a cloth reversing roll or as a concurrent pressure and reversing roll. The aforesaid pressure adjusting device may consist of a threaded spindle and wheel for manual control which permits changing the function of the double-purpose roll in a simple and reliable manner from that of a stenting and reversing roll to that of a simple reversing roll, or vice versa. At the same time, this pressure adjusting means also permits a partial release of the double-purpose roll by causing the same to adopt an intermediary position between that of full contact with its drum and the out-of-contact position. This may become desirable when the tension of the clastic cloth around the double-purpose roll becomes too strong so that the pressure along the line of contact between this roll and the drum strainer becomes too great. By a simple turning of the threaded spindle, a desired portion of the cloth tension can be taken up. This permits an easy control of the pressure exercised by the douhie-purpose roll on the pulp stock thus providing a universal apparatus for thickening all kinds of fibrous suspensions in a very effective manner without the requirement of providing the apparatus with additional rolls.

With these objects and advantageous features in mind, our present invention comprises the arrangement combination and construction of parts, as will be hereinafter fully described with reference to the accompanying drawings in which- Figure l is a side view of an apparatus provided with two drum strainers according to the invention;

Figure 2 shows schematically the arrangement of a somewhat different embodiment of the apparatus according to the invention;

Figure 3 shows another embodiment of the apparatus according to the invention wherein a stenting roll is provided for each of the two drums; and

Figure 4 illustrates yet another embodiment provided with a stenting roll for the second cylinder only.

Referring now to the drawings more in detail, wherein like numerals indicate similar parts, the apparatus is mounted on a machine frame structure 1 and comprises a first large drum strainer 2 and a second drum strainer 3 of smaller diameter. The ratio of the diameters of the first to the second cylinder is, in the embodiments shown in Figures 1, 3 and 4, in the order of 2: 1. Cloth-reversing rolls 4, 5, 6 and 7 are also mounted in the frame structure 1 and guide a broad rubber cloth or wire 8 around each of the drums 2 and 3 in such a manner that the area of contact between the cloth and the drums occupies a considerable portion of the total cylindrical surface of the drums.

While, in the embodiment of Figure 2, the contact segment of the drum surface responds to an angle of about 90 on the first and about 70 on the second drum, the embodiments illustrated in Figures l, 3 and 4 show corresponding angles of more than 180 for the first and about 120 for the second drum, due to the provision of the reversing roll between the two drum strainers.

The stenting roll 9 is pivotally mounted at 21, and tension of the cloth 8 can be adjusted by the threaded adjusting means it]. The endless cloth 8 is set in motion, for instance, by a motor and transmission belt drive 22.

The fibrous suspension is introduced into the feeding box 12 through a feed pipe 11. The feeding box 12 is mounted above the large drum 2 and admits the suspension at 23 to the interspace between cloth 8 and drum 2. Between the cloth 8 and the cylinders 2 and 3, a portion of the liquid contained in the pulp stock is removed by pressure. The removed liquid is squashed out laterally from the drums and the thickened pulp stock is parted from the cloth by means of a doctor or a guard board 13.

The embodiment shown in Figure 2 corresponds essentially to that shown in Figure 1 with the exception that the reversing roll 5 is omitted.

In order to increase the final dry content of the (web) pulp stock, the apparatus according to the embodiment shown in Figure 3 is provided with a press roll 14 arranged adjacent thickener cylinder 2. This press roll 14- is vertically displaceable between two guides 15 by means of a pneumatic pressure device 16 and can thus be pressed against the surface of cylinder 2 and the elastic cloth 8. A second press roll 17 is mounted in frame l for engaging the second thickener cylinder 3. Press roll 17 is pivotally mounted on frame 1 by means of two lateral arms 18 and is equally urged against cylinder 3 and cloth 8 by means of a pneumatic pressure device 19.

In the embodiment shown in Figure 4, cylinder 2 is not provided with an additional press roll. The second cylinder 3 is also not provided with a separate press roll. However, the cloth reversing roll 6 which is mounted stationary in the embodiment shown in Figure 1, is here devised as a double purpose roll. To this end it is pivotally mounted at 24 and can be pressed, by means of its pressure adjusting device 20, against the thickener drum 3. In the latter case, it acts as a press roll and, concurrently, as a cloth reversing roll. The pressure adjusting device 20 in Figure 4 comprises a threaded spindle. If a lesser final dry content is desired, the double purpose roll 6 can be maintained in a partially relieved position relative to the cylinder 3 against the tension of the elastic cloth 8 or can be fully withdrawn from the cylinder 3, thus exercising no pressure at all on the pulp stock between cylinder 3 and belt 8.

A resilient member 25 such as a spring or the like is disposed with the pressure adjusting means 2th to act as an intermediary resilient member imparting a resilience within certain limits to the press roll in the position of the latter relative to the drum strainer in order to yield somewhat if foreign matter enters between the cylinder and the press roll.

The above described embodiments of a thickening apparatus according to the invention make it possible to obtain a high final dry content of the fibrous suspension even if the latter consists of materials from which the liquid can only be removed with difficulty.

It will be understood that this invention is susceptible to further modification and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

What we claim is:

1. Apparatus for thickening fibrous suspensions, comprising a first rotatable drum strainer, an endless elastic conveying means adapted for carrying on one side thereof a web deposited from said fibrous suspension and to be dehydrated, said conveying means being trained onto said first drum strainer to contact a substantial part of the drum surface of the latter, feeding means for feeding said suspension onto said first drum strainer, said feeding means being disposed at the zone where said conveying means comes into contact with said first drum strainer, further rotatable drum strainer contacted by said conveying means on the side thereof carrying said web over a substantial part of the surface of said further drum strainer, said further drum strainer being of smaller diameter than said first drum strainer, guiding rolls inside said endless conveying means, at least one of which guiding rolls is adapted to act as a tensioning roll, and means for driving said endless elastic conveying means, whereby said web is subjected to a greater pressure while in contact with said further drum strainer than it was subjected to while in contact with said first drum strainer.

2. Apparatus as defined in claim 1 further comprising means cooperating with said further drum strainer for exerting additional pressure upon said conveying means against said further drum strainer.

3. Apparatus as defined in claim 1 wherein the ratio of the diameters of said drum strainers is approximately 4. Apparatus for thickening fibrous suspensions, comprising a plurality of rotatable drum strainers, said plurality of drum strainers incorporating at least a first and a second drum strainer, said first drum strainer having a diameter larger than said second drum strainer; an endless elastic conveying means adapted for carrying on one side thereof a web deposited from a fibrous suspension and to be dehydrated; means for guiding and moving said conveying means in such a manner that the same side-of said conveying means first contacts a substantial part of the drum surface of said first drum strainer and thereafter contacts a substantial part of the drum surface of said second drum strainer; and feeding means for feeding the fibrous suspension onto said first drum strainer, said feeding means being disposed at the zone where said conveying means comes into contact with said first drum strainer, whereby the web of fibrous suspension carried by said conveying means is subjected to a greater pressure while in contact with said second drum strainer than it was subjected to while in contact with said first drum strainer.

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